1. Field of the Invention
The present invention relates to rechargeable batteries and in particular to a battery fuel gauge circuit for detecting the capacity of the rechargeable batteries.
2. Description of the Related Art
Currently, portable electronic appliances are becoming more and more common in today's society as the capabilities and uses of such appliances continue to expand. The portable electronic appliances may include, by way of example, laptop computers, cell phones, personal digital assistants (PDAs), pagers, camcorders, digital cameras and other devices. Many portable electronic appliances are powered by rechargeable batteries, i.e., secondary batteries that sometimes can form a rechargeable battery pack. Such rechargeable batteries can include alkaline batteries such as well-known nickel cadmium (Ni—Cd) or nickel metal hydride (Ni-MH) batteries. Recently, lithium ion (Li-ion) batteries have gained more popularity in some high-end portable electronic appliances because they exhibit high energy density, low temperature characteristics, and stable storage capability.
The rechargeable battery pack often includes circuit boards, electronic circuitry, mechanical assemblies and electromechanical protection components. The rechargeable battery pack usually requires an electronic charger for recharging the depleted batteries. The electronic charger may start, ramp, taper or stop the charging current to the rechargeable battery pack and measure its temperature, just to name a few of the functions. Simply speaking, the battery pack is a complex system of components working in harmony to safely deliver power to any type of the above-mentioned portable electronic appliances.
In usage, one of the most common concerns about the rechargeable battery pack is to determine how many “charges” are left in the battery pack, that is, the remaining capacity of the battery pack. In order to determine the capacity of the battery pack, some prior art solutions utilize numerous components and different algorithms, and are costly to be manufactured although higher accuracy of the prediction of the battery pack can be achieved by these solutions. These solutions usually rely on software and analog-to-digital converters (ADCs) that increase the cost and complexity of the portable electronic appliances. As a result, these solutions will be not worth for some small and low cost applications.
Some cheaper solutions with fewer components can be used to predict the remaining capacity of the rechargeable battery pack. The usual drawback of these solutions is that they have low accuracy, low efficiency or bad performance. With these solutions, it is difficult to accurately predict the remaining capacity of the rechargeable batteries.
It is thus desirous to have an apparatus that can provide accurate prediction of the remaining capacity of the rechargeable battery pack without adding complexity and unnecessary cost to the apparatus, and it is to such apparatus the present invention is primarily directed.